1. Field of the Invention
The present invention relates to a stitch control mechanism for a flat knitting machine, for controlling stitch size in knitting a knit fabric on a flat knitting machine.
2. Related Art Statement
In knitting a knit fabric, stitch size is dependent on the down stroke of the needle forming a needle loop lowered by a stitch cam. Generally, two stitch cams are disposed respectively on the opposite sides of a raising cam so as to lower the needle. The stitch cams are supported for vertical movement along the raising cam on a base plate and are moved vertically for positioning by stitch cam moving means. As shown in FIG. 5, a stitch cam 51 is supported on a guide plate 54 having a portion slidably fitted in a slot 53 formed in a base plate 52. A stitch cam positioning cam 57 is supported on the output shaft 56 of a motor 55. A cam roller 58 supported on the guide plate 54 at the upper end of the same is biased toward the stitch cam positioning cam 57 by the contractive force of a spring 59. Another cam roller 60 is supported on the lower end of the guide plate 54. The stitch cam 51 is raised when a stitch cam raising cam plate 61 engages the cam roller 60, and the stitch cam 51 is lowered and the cam roller 58 is brought into contact with the stitch cam positioning cam 57 when the stitch cam raising plate 61 separates from the cam roller 60. The stitch cam positioning cam 57 is turned to raise or lower the stitch cam 51 for positioning through the cam roller 58 and the guide plate 54.
Since the cam roller, which moves together with the stitch cam, and the stitch cam positioning cam are engaged by the contractive force of the spring, the displacement of the cam roller is liable to fall behind the turning motion of the stitch cam positioning cam when the knitting machine operates at a high knitting speed.
A stitch control mechanism shown in FIG. 6 incorporates improvements to overcome such a disadvantage. Similarly to the stitch control mechanism shown in FIG. 5, this stitch control mechanism supports a stitch cam 71 on a guide plate 74 having a portion slidably fitted in a slot 73 formed in a guide plate 74. A cam roller 75 pivotally supported on the guide plate 74 engages a stitch cam control lever 76 supported for swing motion on a shaft 77. A cam roller 78 is supported pivotally on the stitch cam control lever 76 in the middle portion of the same and the cam roller 78 is fitted in the spiral cam groove 79 of a stitch cam control cam 80. The stitch cam control cam 80 is fixed to the output shaft 82 of a motor 81. The stitch cam control cam 80 is turned by the motor 81 and, consequently, the stitch cam control lever 76 swings to move the guide plate 74 supporting the cam roller 75 so that the stitch cam 71 is raised or lowered. A small clearance must be formed between the cam roller 78 supported on the stitch cam control lever 76 and the side surface of the spiral cam groove 79 of the stitch cam control cam 80 to allow the cam roller 78 to move along the spiral cam groove 79. Accordingly, the rotation of the motor 81, hence the rotation of the stitch cam control cam 80, may not accurately be transmitted in a linear motion to the stitch cam 71.
Since the spring of the former conventional stitch control mechanism biases the stitch cam continuously downward as stated above, the stitch cam control cam and the cam roller supported on the guide plate supporting the stitch cam must be separated from each other for every loop size adjustment or the motor must be of a large output capacity. Accordingly, the carriage is formed inevitably in a comparatively large size and hence a comparatively large driving mechanism is required.
Furthermore, the spring for biasing the stitch cam downward, the cam plate for separating the cam roller provided on the guide plate supporting the stitch cam from the stitch cam control cam, and the mechanism for operating those components, which are essential to this conventional stitch control mechanism, increase the size and weight of the stitch control mechanism, which is an impediment to the enhancement of the knitting speed of the knitting machine. Still further, since a clearance is formed between the stitch cam control cam and the cam roller, i.e., a stitch cam moving member, the cam roller is unable to follow the movement of the stitch cam control cam without delay.